1. Field of the Invention
The present invention relates to multimetal oxide compositions of the formula I EQU [A].sub.p [B].sub.q (I),
where
A is Mo.sub.12 X.sub.a.sup.1 X.sub.b.sup.2 X.sub.c.sup.3 X.sub.d.sup.4 S.sub.e X.sub.f.sup.5 O.sub.x PA1 B is X.sub.g.sup.6 X.sub.h.sup.7 O.sub.y
X.sup.1 is phosphorus, arsenic, boron, germanium and/or silicon, PA0 X.sup.2 is vanadium, niobium and/or tungsten, PA0 X.sup.3 is hydrogen, of which up to 97 mol % may have been replaced by potassium, rubidium, cesium and/or ammonium (NH.sub.4), PA0 X.sup.4 is antimony and/or bismuth, PA0 X.sup.5 is rhenium and/or rhodium, PA0 X.sup.6 is copper, iron, cobalt, nickel, zinc, cadmium, manganese, magnesium, calcium, strontium and/or barium, PA0 X.sup.7 is niobium, tantalum and/or antimony, PA0 a is from 1 to 6, preferably from 1 to 3, particularly preferably from 1.5 to 2.5 PA0 b is from 0 to 6, preferably from 0.2 to 4, particularly preferably from 0.5 to 2 PA0 c is from 3 to 5, PA0 d is from 0 to 6, preferably from 0 to 3, particularly preferably from 0.5 to 1.5 PA0 e is from 0 to 3, preferably from 0.01 to 1, particularly preferably from 0.01 to 0.2, PA0 f is from 0 to 3, preferably from 0.01 to 1, particularly preferably from 0.01 to 0.5, PA0 g is from 0.5 to 1.5, preferably from 0.9 to 1.1, PA0 is from 2 to 4, preferably from 2 to 3, particularly preferably from 2 to 2.5, PA0 x and y are numbers determined by the valency and frequency of the elements other than oxygen in I, and PA0 p and q are numbers other than zero whose ratio p/q is from 12:0.1 to 12:48, preferably from 12:0.25 to 12:12, particularly preferably from 12:0.5 to 12:4,
which contain component [A].sub.p in the form of three-dimensionally extended regions A of the chemical composition EQU A Mo.sub.12 X.sub.a.sup.1 X.sub.b.sup.2 X.sub.c.sup.3 X.sub.d.sup.4 S.sub.e X.sub.f.sup.5 O.sub.x
which are delimited from their local environment due to their chemical composition which is different from their local environment, and component [B].sub.q in the form of three-dimensionally extended regions B of the chemical composition EQU B X.sub.g.sup.6 X.sub.h.sup.7 O.sub.y
which are delimited from their local environment due to their chemical composition which is different from their local environment, where the regions A and B are distributed relative to one another as mixture of finely divided A and finely divided B.
The present invention also relates to a process for the preparation of these compositions, and to their use.
2. Description of the Prior Art
EP-A 442 517 and EP-A 424 900 relate to multimetal oxide compositions whose empirical elemental composition corresponds to that of the novel multimetal oxide compositions.
These multimetal oxide compositions are prepared by converting suitable sources of the constituents of the desired multimetal oxide compositions in the requisite amounts into an intimate dry mix, and subsequently calcining the latter at elevated temperature for several hours.
The resultant multimetal oxide compositions are recommended, inter alia, as catalysts for the preparation of methacrylic acid from methacrolein by gas-phase catalytic oxidation. However, the multimetal oxide compositions of this prior art have the disadvantage that both their activity and the selectivity in the formation of methacrylic acid for a given conversion are not entirely satisfactory. The same applies to the reproducibility of their preparation and to their service lives, which are particularly unsatisfactory if the reaction gases comprising methacrolein as the principal constituent contain organic acids as secondary constituents.